Pumps with heat exchanger for pumping slurries



y 9, 1967 J. F. CAMPOLONG 3,318,253

PUMPS WITH HEAT EXCHANGER' FOR PUMPING SLURRIES Filed Jan. 21, 1965 United States Patent O 3,318,253 PUMPS WITH HEAT EXCHANGER FOR PUMPING SLURRIES Joseph F. Campolong, Windham County, Conn., assignor to Pall Corporation, Glen Cove, N.Y., a corporation of New York Filed Jan. 21, 1965, Ser. No. 427,008 18 Claims. (Cl. 10s-s7 This invention relates to a canned or close-coupled motor pump, i.e., a pump wherein the pump chamber and motor are enclosed in a single housing, and having a heat exchanger for cooling the liquid contained in the motor rotor chamber thereof. More specifically, this invention relates to a canned pump especially designed for the pumping of slurries or suspensions, wherein the motor rotor compartment is sealed off from the pump chamber, and wherein a heat exchanger is provided for passing liquid from the pump chamber in heat-exchange relationship with liquid from the motor rotor chamber, the heat exchanger having a porous member separating the two liquids for pressure compensation therebetween.

Canned pumps may be divided into two types: the fluid bypass or circulation type, wherein the motor rotor chamber is in direct and continuous fluid flow connection with the pump chamber, with a by-pass line for circulation of the pumped liquid freely therethrough, to lubricate and cool the motor rotor chamber. The other type of canned pump is the sealed motor type, wherein the motor rotor compartment, and usually also the stator compartment, are more or less completely sealed off from the pump chamber, so that the liquid contained in the motor rotor chamber for purposes of cooling and lubricating of the motor, even though it be the same liquid as the pumped liquid, is separated from the pumped liquid.

The former type of pump has, of course many advantages over the sealed type. There is no need for seals between the motor rotor chamber and the pump chamber, and there is also no difliculty in cooling the motor, as a suflicient flow of the pumped liquid can be diverted through the motor rotor chamber to meet the need, and then returned to the line.

On the other hand, a sealed motor is of greater use when dealing with the pumping of liquids which are either highly corrosive, in which case a different liquid can be used as the coolant or lubricant, or which contain substantial amounts of suspended solids which could readily clog the motor bearings and cause increased frictional wear, as well as prevent the proper cooling of the various small diameter portions of the motor. When dealing with solid suspensions, it is, of course, necessary to prevent any solids from entering the support bearings of the shaft or from being lodged in the rather narrow space separating the rotor from the stator. However, with a sealed motor rotor chamber, it is of course necessary to cool the liquid in the motor rotor chamber to remove the heat generated by friction as well as by hysteresis losses. It is also necessary either to provide seals between the motor rotor chamber and the pump chamber that are virtually leakproof, to prevent flow past the seal from one side or the other as pressures vary in these respective chambers, or else to provide breather vents there for pressure equalization. Neither procedure is entirely satisfactory, since foreign matter can enter in the latter case, and since Wear erode any tight seal with time, in the former case.

The prior art has resorted to the use of heat exchangers for cooling the motor rotor liquid. In some cases, the heat exchanger is a coil externally of the housing, to permit heat exchange with the atmosphere. U.S. Patent No. 2,690,946 discloses an electric motor, which is not necessarily connected to a pump, but in which the motor rotor chamber fluid is cooled in a heat exchanger, located 3,318,253 Patented May 9, 1967 externally of the motor housing, by an external fluid. In U.S. Patents Nos. 2,913,988 and 2,964,649 to O. P. Steel III et al., the motor rotor chamber liquid is cooled in an external heat exchanger by a special heat exchange fluid. Similarly, in U.S. Patent No. 2,598,547, to Ivanoff, a canned pump is disclosed having an external heat exchanger for the motor rotor chamber fluid. In all of these systems, the motor rotor liquid is completely sealed off from the pumped liquid. In U.S. Patents Nos. 2,687,695, to Blom et al., and 2,871,791 to Litzenberg, pumps are disclosed wherein the motor rotor chamber is in fluid flow connection with the pump chamber, and wherein the pump liquid may be freely exchanged with the motor rotor chamber liquid for cooling and replenishing.

In accordance with the present invention, a sealed motor type of system for cooling the cooling and lubricating liquid in the motor rotor chamber of a canned pump is provided, which also provides for pressure compensation between the pump chamber and the motor rotor chamber, and which utilizes the pumped liquid as the coolant liquid without the need for circulation thereof through the motor rotor chamber. This system thus combines the advantages of a sealed motor type, from the standpoint of motor rotor chamber cooling and lubrication without contamination, with the advantages of a by-pass type, from the standpoint of pumped liquid volume availability in cooling. and pressure equalization.

The cooling system of the invention comprises a heat exchanger having two sides for heat exchange, one side being part of a coolant-pumped liquid flow circuit including the pump chamber, the second side being part of a separate and distinct sealed motor type of fluid flow circuit including the motor rotor chamber of the canned pump, separated by a porous member constituting a heat transferring barrier allowing the compensating fluid flow of liquid between the two sides of the heat exchanger while blocking passage of any solid particle suspended within the pumped liquid. The motor rotor chamber is otherwise sealed off from direct fluid flow connection with the pump chamber, and because of the pressure compensating feature such seals are more than normally leakproof, since the buildup of excessive pressure differentials across the seals is effectively inhibited. Therefore, this system allows the interchange of heat, while minimizing interchange of fluid, between the pump fluid circuit of the canned pump and the motor rotor chamber fluid circuit of the canned pump. At the same time, there is a continuously available entry for pumped fluid minus any solids that may be suspended therein into the motor rotor chamber, to replenish fluid that may be lost for any reason, and thus ensure a full supply of such fluid at all times for cooling and lubrication.

The heat exchanger is so designed as to present sufficient surface area for the transfer of the necessary amount of heat to keep the motor rotor chamber fluid 0001. This area is easily computed, using conventional heat exchanger principles, taking into account the heat conductivity across the porous member of the heat exchanger, the heat capacity of the fluid being circulated,

and the volume and rate of flow of such fluids therethrough. The flow through each of the two sides of the heat exchanger is determined by the heat transfer load necessary to cool the motor and by the temperature of the pumped fluid. The continuous flow through the heat exchanger, especially on the pump side, serves to clean the filter surface as in a wash filter. This prevents the buildup of a cake on the slurry side of the filter, which would otherwise form and eventually clog the filter pores.

The canned pump of the invention comprises, in combination, a housing enclosing a pump chamber, a motor rotor chamber and a stator chamber, the pump chamber being separated from both the motor stator and the motor rotor chambers by fluid-tight seals, and a heat exchanger having two chambers separated by a porous member, each chamber having an inlet and an outlet, one chamber being connected in a first fluid flow circuit including the motor rotor chamber, and the other chamber being connected in a second fluid flow circuit including the pump chamber, the sole normally available fluid connection between the circuits being through the porous member.

Preferably, circulating means such as an impeller or turbine is provided in the fluid flow circuit including the motor rotor chamber, to aid in circulating the lubrication and cooling fluid through the heat exchanger. In this preferred structure, the inlet to the heat exchanger is connected to the exhaust side of the circulating means, and the outlet from the heat exchanger is connected to the suction side of the circulating means. The inlet to the other side of the heat exchanger is connected to a relatively high pressure portion of the pump chamber, as on the exhaust side of the pump means, and the outlet from that side of the heat exchanger is connected to a place of lower pressure in the pump chamber, as on the suction side of the pump means.

The heat exchanger can be disposed either externally of the pump housing, in a separate housing, or internally in a common housing for the pump as well. This is a noncritical design feature, that will be determined by space requirements and accessibility for servicing. The motor rotor chamber and one heat exchanger chamber can be combined in one and/ or the pump chamber and the other heat exchanger chamber can be combined in one, when the pump and heat exchanger are in a common housing.

A common type of canned pump of the sealed motor type includes a wall separating the pump chamber from the motor rotor chamber, supporting the motor rotor shaft and shaft bearings, and through which the rotor shaft extends. Seals must be provided between the rotor shaft and the wall to prevent leakage between the pump chamber and the motor rotor chamber. The preferred seal is of the barrier type. When operating with this type of seal, it is preferred that the fluid pressure on the motor rotor chamber side of the seal be somewhat higher than the fluid pressure on the pump chamber side of the seal to ensure that none of the pumped slurry can slip past the seal into the motor rotor chamber. This positive fluid pressure differential is provided in the pump of the invention by connecting the fluid circuit that includes the pump chamber and one side of the heat exchanger to the exhaust side of the pump means, such that the pressure in the rotor chamber is of the desired value. The pressure differential between the motor rotor chamber and the pump chamber will be determined by the pressure in the fluid circuit including the pump chamber and the heat exchanger, any pressure drop across the porous member thereof, and the pressure in the fluid along the circuit including the motor rotor chamber.

This heat exchanger system is suitable for use with any type of canned pump. The most common type of pump is the centrifugal or impeller pump, wherein the pump means is a centrifugal impeller driven by the motor rotor shaft. The pumped fluid enters the central eye of the impeller, and is exhausted, at a higher velocity and pressure, from the ends of the radial arms of the impeller. However, other types of pump means may be used in the combination described above such as gears, as in the gear pump disclosed and described for example in US. Patent No. 2,825,286, to White, wherein the rotor shaft drives a series of gears which impel the fluid through the pump chamber, or a turbine, as in turbine pumps, or pulsating diaphragms. Many other types of pump means will be evident to those skilled in this art.

The porous member is of a heat exchange material, chosen so as to have a pore diameter small enough to prevent the passage of any slurried, or suspended, solids or other foreign solid matter in the fluid being pumped, but which will allow the passage of the liquid between the first and second sides of the heat exchanger, if necessary, in any direction, dependent upon the pressure differential across the porous member. If the pressure in the motor rotor chamber exceeds the pressure in the pump chamber by more than the desired amount, the liquid will flow out through the porous member into the pump circuit. If, on the other hand, the amount of fluid in the motor rot-or chamber drops to below a certain level, so that the pressure therein decreases, the pumped liquid will then be able to pass through the porous member into the motor rotor chamber circuit, to replenish the supply of liquid therein. This invention thereby automatically limits the pressure differential between the pump and motor rotor chambers, and ensures a sufiicient amount of lubricating fluid in the motor rotor chamber, while preventing the passage of any solid particles into the rotor compartment.

The heat exchanger for use in this invention may be of any of the fluid flow types, for example, a concentric tube heat exchanger, where all or part of the inner tube is formed of the porous construction. Alternatively, the heat exchanger may be a shell-and-tube exchanger, wherein all of the tubes are formed of porous material, or wherein only one or some of the tubes are of this porous construction, and the other of conventional construction. A plate type heat exchanger, wherein all or only part of the plate is of porous construction, is also within the purview of the invention. A very simple type of heat exchanger is a chamber separated into two parts by a porous wall. Another simple and available type is a cylindrical or tubular filter assembly, the pumped fluid being circulated on one side of the filter, and the motor rotor fluid being circulated on the other side of the filter.

It is also within the purview of this invention to have a plurality of heat exchangers, where only one or some of the exchangers have the porous construction. Similarly, the operation of the exchanger is not critical to this invention. For example, the flow may be parallel or countercurrent, although the latter is of course preferred. In the case of the plate and shell-and-tube exchanger, cross flow can also be possible. Any and all designs of heat exchangers are included within the purview of this invention, the only limitation being that at least a portion of the heat exchanger surface be of a porous construction.

The dimensions of the heat exchanger will depend first on the heat load the exchanger will have to carry, i.e., the amount of heat that must be transferred across the heat exchange member between the two sides of the exchanger. This, of course, is dependent on the size of the pump motor and the amount of heat it generates. The second design variable will be the temperature difference between the pumped fluid and the motor rotor chamber fluid; the third design variable will be the conductivity of the material forming the heat exchange member. The fourth design variable will be the flow pattern of the two fluids in the exchanger, which is determined by the type of exchanger shown.

The handling of these variables in the design of heat exchangers is well known, and methods of computing the proper dimensions are given in Perry, Handbook of Chemical Engineering, 3d edition, Section 6.

As stated above, even when all separating walls of the heat exchanger are formed in a porous construction, the flow across the walls is negligible, compared to the flow through the exchanger. Accordingly, heat transfer is across or through the porous member, and is not significantly affected by fluid flow through the member.

Thus, an important factor in determining the rate of heat transfer is the material from which the porous member is formed. The preferred material is a metal, the exact kind depending upon the temperature and pressure of operation and the fluids being heat exchanged. The most common material is carbon steel; however, for special purposes, other materials such as high alloy steels, the various forms of iron, copper, brass, and nickel alloys have been used.

The porous member can be formed from any of the materials commonly used for heat exchangers. Preferred materials for maximum heat exchange would be a solid metal plate containing minute punched holes, or sintered porous filter or bearing materials. However, when work. ing with very fine suspended particles, it is frequently necessary to use a finer filter than would be possible with a punched metal plate. Other preferred metallic materials include woven wire mesh, of the type disclosed for filter use in US. Patent No. 2,925,650, porous sintered metal such as disclosed in US. Patent No. 2,554,343 or synthetic plates, suitable for very fine particles. Various nonmetallic porous materials which may be used include porous sintered synthetic resin plates, paper, woven glass fiber, ceramics, natural or synthetic fabrics, unwoven fibrous bats and tapered-pore filters as described in US. Patent No. 3,158,532. I

The material used will depend upon the chemical properties of the pumped fluid, the desired heat exchange rate, the pressure and temperature conditions, and the size of the suspended particles in the slurry being pumped. When a porous material of relatively low heat conductivity is use-d, such as glass or ceramics, it may be necessary to employ members supplying additional heat transfer capacity, such as solid metal plates or fins.

The attached drawing shows a preferred embodiment of canned pumps of the centrifugal impeller type incorrpo rating a concentric tubular assembly as an external heat exchanger including a filter element as the porous member of the heat exchanger.

As shown in this embodiment, the heat exchanger and the pump are enclosed within a common housing 95.

The pump shown in the drawing comprises a housing formed in two sections: the motor section 14, and the pump section 15, bolted together by bolts 17. The motor section 14 is in two sections 11 and 16, which are also bolted together by bolts 18 for ease of maintenance. The rear of the motor section is closed off by back-up plate 13, which is also bolted on by bolts 12.

The pump section 15 includes a pump chamber 22 having an outlet 1-9 and an inlet 20, and an impeller 21 is located in the chamber 22 in fluid flow-intercepting relationship between the inlet and outlet. The impeller has an internal volute 26. The pump section 15 also has a volute 7 formed in the pump chamber 22 complementing the impeller volute 26.

The motor section contains a motor rotor chamber 31, which is closed off from the pump chamber 22 by the end plate 30. Plate 30, at its external periphery, is held by the ledge 32 on the pump section housing 15 against the thrust plate gasket 34, and the entire assembly of plate 30 and gasket 34 are held in a fluid-tight seal between housing sections 14 and 15 by bolts 17.

It is important to prevent any of the suspended solid material from entering the motor rotor chamber. It is of the greatest importance to keep the bearing channels and surfaces and the narrow space between the motor rotor and the stator chambers free of solid particles; the tiny particles could very readily jam and clog up the channels and spaces thereby preventing proper circulation of the fluid and lubrication of the rotor. This is especially true in the bearing channels 45 and 53 where the formation of deposits from the slurry material could very quickly cause a great increase in frictional force on the rotor, slowing it down or completely stopping it. To prevent any leakage between the pump and motor rotor chambers, gaskets 34 and 34 are provided in the joints at ledge 32 of pump housing 15 and face 33 of motor housing 14, and end piece 30, and a lip seal 47 is provided as described below.

A support bearing 46 is press-fitted into a central passage 37 in end plate 30. Rotor shaft 28 passes through and is rotatably supported by the bearing 46 at its front end. A hearing retainer 50 is connected to the end of stator cup 40 abutting back-up plate 13 and holds therein bearing 51 which supports the back end of shaft 28. A barrier seal, in this embodiment a lip seal 47, is located between the impeller shaft 28 and an indentation in the passage 37 of the end plate 30, sealing off the motor rotor chamber 31 from the impeller chamber 22. Bearing lubrication space 44 is defined in passage 3 between the front end of bearing 45 and lip seal 47.

The impeller 21 is attached to drive shaft 28 by bolt 25, which is threaded into a socket in shaft 28. A necked-down portion of the shaft 28 extends through an opening 29 at the back of the impeller 21. The rotor 42 is fixed to the shaft 28, to rotate therewith.

The shaft 28 has a central channel 35 running from the rear of the shaft to a position adjacent the front end of the shaft, beyond the bearing 46. Radial channel 27 in the shaft connects the central channel 35 to the bearing lubrication space 44. A secondary impeller, the radial arms 43 of which enclose channels 48 connecting the central channel 35 of the shaft with the motor rotor chamber 31, is attached to the shaft 28. The back end of the central channel 35. opens into bearing lubrication space 52 formed within bearing holder 50.

The lubrication spaces 44 and 52 communicate directly with the motor rotor chamber 31 through the longitudinal and radial channels 45 and 53, respectively.

Stator chamber 38 is an annular chamber just inside of the motor section housing 14, defined by stator cup 40, and contains the stator 39. The stator armature 39 is connected to a source of electrical power (not shown) via electrical wires 60.

The heat exchanger is a concentric tube heat exchanger having an outer tube or housing 61 with end caps 62 and 63 held in place by double-end threaded bolt 71 and nuts 72 with a gasket ring seal 73 at each end to prevent leakage. An inner porous walled tube 64, constituting the porous member of the heat exchanger is formed of a cylindrical filter element made of porous stainless steel, made under US. Patent No. 554,343, and having a mean pore size of 12 microns, with a surface area of 78 sq. ins. The filter element has end caps 67 welded thereon and is centered and held in place within the outer tube 61 by means of the tubular bosses 70, on the inner faces of the outer end caps 62 and 63, which protrude into the central openings of the end caps 67. The ends of the tube 64 are sealed to outer end caps 62 and 63 by gaskets 6S. Annular chamber 65 is formed between the inner tube 64 and outer tube 61, and a central chamber 66 is enclosed within the tube 64.

In this embodiment, a first heat exchange flow circuit A is formed including the motor rotor chamber 31, the interior of the inner tube 64 of the heat exchanger, and the connecting conduits 75 and 78. One end of conduit 75 is attached to back-up plate 13 and then to the motor rotor chamber 31. The other end of conduit 75 is attached to the end cap 63, and is in flow connection with channel 77 through the end cap to the interior of the inner tube 64. Conduit 78, has one end in fluid flow connection with the central channel 35 in the shaft 28 through back-up plate 13 and space 52, and the other end is connected to the conduit 79 through end cap 62, which in turn is connected to the interior of tube 64.

The second flow circuit B through the heat exchanger includes the annular chamber 65 of the heat exchanger and is connected to the impeller chamber via the connecting conduits 80 and 81. The conduit 80 is connected at one end to a channel 69, through the end cap 62, which connects to the annular chamber 65, and at the other end to a relatively high pressure portion of the impeller chamber 22 through an opening in the pump housing 15. Conduit 81 is connected at one end to a channel 75 through end cap 63, which in turn connects with annular chamber 65, and at its other end to a relatively lower pressure section of the impeller chamber 22 through an opening in the pump housing 15.

In operation, the slurry or suspension enters the pump housing through inlet '20. Before the pump is turned on, fluid is allowed to fill the impeller chamber 22, and then passes out through conduits 80 and 81 to fill the annular chamber 65 of the heat exchanger. The slurrycarrying liquid will then pass through the porous-walled tube 64, which filters out the solid particles, and fills the central chamber 66; it will then pass out through the conduits 75 and.78 and fill the motor rotor chamber 31 and central channel 35.

When the system is all filled, the pump is turned on. As the impeller 21 rotates, the secondary impeller 43 also rotates, which aids in circulating the fluid through the central shaft, around the motor rotor chamber 31 and through tube 64 of the heat exchanger. In the heat exchanger the motor rotor chamber lubricating liquid is cooled by the pumped slurry passing countercurently through the annular portion 65, the cooled lubricating liquid then returning to the central channel 35 of the shaft through space 52. A portion of the fluid also passes through bearings 46 and 51 for lubricating and cooling.

The pumped fluid enters through inlet and passes into the eye of the impeller, from which it enters the impeller chamber 22 at an increased pressure. A minor portion of the slurry, enters the inlet conduit 80 at a point of higher pressure in the impelller chamber than at the outlet conduit 81. The fluid then passes into the annular chamber 65 of the heat exchanger, through channel 75 into conduit 81, from which it re-enters the pump chamber 22 at a point of lower pressure than at the conduit 80.

The position in the pump chamber 22 where the flow to the heat exchanger is tapped is selected so as to maintain a slightly higher pressure on the motor rotor chamher side of the lip seal 47 between the motor rotor and pump chambers. The pressure at any given portion of the pump chamber 22 is proportional to the distance from the center of the impeller, so that the conduit 80 is attached to the housing at a point of greater distance from the center of the impeller 21 than is conduit 81. The pressure in the motor rotor chamber 31 is determined by the pressure at the tap-off point of conduit 80 in the pump chamber less the pressure drop along the flow lines between the pump and motor rotor chambers and the heat exchanger and across the porous member 64. Ideally, the pressure differential across the seal 47 should be as small as practicable.

The major proportions of the slurry is spun out through the volute 26 of the impeller into the volute 27 in the pump section housing 15 and then out through the outlet 19 at the desired pressure.

If the pore diameter is extremely small, it may be necessary to fill the rotor compartment separately with liquid before starting the pump. For this purpose, inlet 90 and gate valve 91 are provided, for filling the rotor chamber before operating the pump. The valve is closed during operation.

The various parts of the housing 11 are shown as being bolted together for ease of maintenance in breaking down the entire unit. However, it is also possible to weld, braze or solder the sections as shown together or pressfit them with an adhesive, or to cast the housing in two axial halves, and then connect them as desired.

The above-described embodiment is merely exemplary of this invention, the scope of which is defined by the following claims.

I claim:

1. A heat exchanger for pumps having two sides for heat exchange, one side having an inlet and an outlet adapted to be connected to a coolant-pumped fluid flow circuit including a pump chamber, the second side having an inlet and an outlet adapted to be connected to a fluid flow circuit including the motor rotor chamber of the pump, a porous member separating the two sides and constituting a heat transferring barrier allowing flow of fluid between the two sides of the heat exchanger, while blocking passage of any solid particles suspended within the pumped liquid.

2. The heat exchanger of claim 1 wherein the porous member comprises a filter.

3. The heat exchanger of claim 1 wherein the porous member is a tube disposed within an outer concentric tube, defining an inner and an outer annular chamber.

4. A canned pump comprising in combination, a housing enclosing a pump chamber, a motor rotor chamber and a stator chamber, the pump chamber being separated from the motor rotor chamber by fluid tight seals, and a heat exchanger according to claim 1; the inlet and the outlet of the first side'of the heat exchanger being connected to a first fluid flow circuit including the pump chamber; and the inlet and the outlet of the second side of the heat exchanger being connected to allow circuit including the motor rotor chamber of the pump, at least a portion of the pumped fluid in the pump chamber passing through the first flow circuit on one side of the porous member in heat exchange relationship with fluid in the second flow circuit.

5. A canned pump in accordance with claim 4 comprising circulating means in the first fluid flow circuit.

6. A canned pump is accordance with claim 4 in which the porous member is a wall.

7. A canned pump in accordance with claim 4 in which the porous member comprises a filter.

8. A canned pump in accordance with claim 4 in which the heat exchanger is also enclosed within the housing.

9. A canned pump in accordance with claim 4 in which the heat exchanger is enclosed within a separate housing.

10. A canned pump comprising, in combination, a housing having a pump chamber with an inlet and an outlet, a motor rotor chamber and a motor stator chamber, the pump chamber being sealed off from the other chambers, and a porous-walled heat exchanger comprising a heat exchanger housing and a porous member dividing the heat exchanger housing into two sides, fluid flow means connecting the first side of the heat exchanger with the pump chamber, and fluid flow means connecting the second side with the motor rotor chamber, whereby fluid flowing through the rotor section is in heat exchange relationship across the porous member with the fluid passing through the pump chamber.

11. A canned pump comprising, in combination, a pump housing having formed therein a pump chamber having an inlet and an outlet, a motor rotor chamber, a wall member having an aperture separating the pump chamber and the motor rotor chamber, and a motor stator chamber disposed annularly around the motor rotor chamber, a motor shaft disposed within said rotor and pump chambers and passing through the aperture in the wall member, a motor rotor fixedly attached to the shaft within the motor rotor chamber, the motor rotor chamber being sealed off from direct fluid flow connection with the pump chamber, and a heat exchanger comprising a heat exchanger housing, and a porous member dividing the heat exchanger housing into two sides, each side having an 1nlet and an outlet, the inlet to the first side being connected to a point of relatively high fluid pressure in the pump chamber, the outlet from the first side being connected to a point of relatively low fluid pressure in the pump chamber, the inlet to the second side being connected to a point of relatively high fluid pressure in the motor rotor chamber and the outlet from the second side to a point of lower fluid pressure in the motor rotor chamber.

12. The combination of claim 11 having a circulating impeller within the motor rotor chamber attached to and driven by the motor shaft, the inlet to the second side of the heat exchanger being on the exhaust side of the circulating impeller, and the outlet from the second side being on the suction side of the circulating impeller, whereby the fluid is circulated thereby through the motor rotor chamber and the second side of the heat exchanger.

13 The combination of claim 11 wherein the porous member comprises a porous tube disposed within the heat exchanger housing.

14. The combination of claim 13 wherein the heat exchanger housing comprises an outer tube enclosing the porous tube.

15. The combination of claim 11 wherein the heat exchanger is of the shell-and-tube type and wherein at least one of the tubes has a porous Wall.

16. The combination of claim 11 including a centrifugal impeller fixedly attached to the shaft within the pump chamber, disposed in flow-intercepting relationship between the pump inlet and the pump outlet, and a seal in the aperture between the shaft and the Wall member to prevent leakage of fluid between the pump and motor rotor chambers, and wherein the inlet to the first side of the heat exchanger is connected to the pump chamber at a point farther from the axis of rotation of the impeller than the outlet from the first side.

17. In combination, a canned centrifugal pump comprising a pump housing having an impeller chamber having an inlet and an outlet, a motor rotor chamber and a motor stator chamber, the pump and motor rotor chambers being sealed off from fluid flow connection with each other, a drive shaft disposed within the motor rotor chamber and the impeller chamber, support bearings within the housing for rotatively supporting the drive shaft, a rotor attached to the drive shaft within the motor rotor chamber, an impeller attached to the drive shaft in the pump chamber in fluid flow-intercepting relationship to the inlet and the outlet, a wall member separating said impeller chamber from said motor rotor chamber having an aperture therethrough through which the drive shaft extends, a barrier seal in the aperture between said Wall member and said shaft, sealing the impeller chamber from the motor rotor chamber, a central channel through said drive shaft for fluid passage therethrough, a secondary centrifugal impeller attached to the drive shaft within the motor rotor chamber in fluid flow connection with the central channel whereby the central channel is in fluid flow connection with the suction side of the secondary impeller, the motor rotor chamber being on the exhaust side of the secondary impeller, and a porous-walled heat exchanger comprising a heat exchanger housing, a porous member permitting the passage of fluid but inhibiting the passage of any solids suspended in the fluid, an inlet to the first side in fluid flow connection with a relatively high fluid pressure portion of the impeller chamber, an outlet from said first side in fluid flow connection with a relatively low fluid pressure portion of the impeller chamber, an inlet to said second side in fluid flow connection to the rotor chamber and an outlet from said second side in fluid flow connection with the second open portion of the central channel through the drive shaft, the high pressure portion of the impeller chamber being selected to provide a fluid pressure on the motor rotor chamber side of the barrier seal slightly greater than the fluid pressure on the impeller chamber side of the barrier seal.

18. A canned pump comprising a housing having a pump chamber, motor rotor chamber and a stator chamber, the motor rotor chamber being sealed off from the pump chamber so as to prevent the direct passage of fluid between the pump chamber and the motor rotor chamber, and a heat exchanger having a porous heat-exchanging wall dividing the heat exchanger into two sides, one side being connected in a first flow circuit including the rotor chamber, the second side being connected in a second flow circuit including the pump chamber, the porous heatexchanging wall providing the only fluid connection between the first flow circuit and the second flow circuit, allowing the passage of fluid therethrough, but inhibiting the passage of suspended solids therethrough.

ROBERT M. WALKER, Primary Examiner. 

1. A HEAT EXCHANGER FOR PUMPS HAVING TWO SIDES FOR HEAT EXCHANGE, ONE SIDE HAVING AN INLET AND AN OUTLET ADAPTED TO BE CONNECTED TO A COOLANT-PUMPED FLUID FLOW CIRCUIT INCLUDING A PUMP CHAMBER, THE SECOND SIDE HAVING AN INLET AND AN OUTLET ADAPTED TO BE CONNECTED TO A FLUID FLOW CIRCUIT INCLUDING THE MOTOR ROTOR CHAMBER OF THE PUMP, A POROUS MEMBER SEPARATING THE TWO SIDES AND CONSTITUTING A HEAT TRANSFERRING BARRIER ALLOWING FLOW OF 